Machine for making thin paper

ABSTRACT

A paper-making machine comprises a forming section, in which a web is formed on a moving foraminous member, a heated, rotating &#34;Yankee&#34; dryer cylinder positioned in proximate, spaced relation to a pick-up location on the foraminous member, and a combination rotating suction pickup, couch, transfer and press roll positioned in light engagement with the foraminous member at the pick-up location and in de-watering pressure engagement against the surface of the Yankee dryer cylinder. The combination roll picks the web of the foraminous member, transfers it to the Yankee dryer cylinder and presses it in a press nip with the Yankee dryer cylinder to further remove liquid prior to drying on the cylinder. One or more additional presses can be used in conjunction with the Yankee dryer cylinder downstream from the combination roll.

1 26, 7 N. P. 'SKEPPSTEDT 3,694,131 1 MACHINE FOR MAKING THIN PAPER Filed Jan. 18, 1971 GTO iiiii an? W I N VENTOR.

N LS PETRI SKEPPSTEDT United "States Patent 01 ice 3,694,311 Patented Sept. 26, 1972 3,694,311 MACHINE FOR MAKING THIN PAPER Nils Petri Skeppstedt, Ulvsby, Sweden, assignor to Aktiebolaget Karstads Mekaniska Werkstad, Karlstad, Sweden Filed Jan. 18, 1971, Ser. No. 107,114 Int. Cl. D21f 5/00, 9/00 US. Cl. 162-290 7 Claims ABSTRACT OF THE DISCLOSURE A paper-making machine comprises a forming section, in which a web is formed on a moving foraminous memher, a heated, rotating Yankee dryer cylinder positioned in proximate, spaced relation to a pick-up location on the foraminous member, and a combination rotating suction pickup, couch, transfer and press roll positioned in light engagement with the foraminous member at the pick-up location and in de-watering pressure engagement against the surface of the Yankee dryer cylinder. The combination roll picks the web off the foraminous member, transfers it to the Yankee dryer cylinder and presses it in a press nip with the Yankee dryer cylinder to further remove liquid prior to drying on the cylinder. One or more additional presses can be used in conjunction with the Yankee dryer cylinder downstream from the combination rotll.

BACKGROUND OF THE INVENTION This invention relates to a paper-making machine of a type that involves the use of a so-called Yankee dryer cylinder and, in particular, to a machine that is particular- 1y suitable for manufacturing high quality, light weight paper webs of the tissue and monoglazed types but which also can be employed to advantage in manufacturing somewhat heavier papers.

In the most common type of paper-making machines, the so-called Fourdrinier type machines, paper-making fibers in a highly diluted suspension in a liquid are deposited onto an upper, substantially horizontal run of an endless moving woven wire or fabric belt. As the belt moves along the straight run from the point of deposition of the fiber suspension, liquid drains through the foramnious belt leaving a wet and fragile web on the belt. The web is removed from the belt either at the so-called couch roll or at a point along an inclined run of the belt between the couch roll and a turning or drive roll located below and in front of the couch roll. The operation of picking the weboff the wire and transferring it to the press section of the paper-making machine has frequently been the most troublesome point in the paper-making equipment, since the web is still very wet and can easily break.

A common type of pickup and transfer system employs a suction pickup roll that is enclosed in a loop of felt and sucks the felt off the foraminous belt. The pick-up felt is maintained relatively moist and is usually of a relatively close and smooth weave so that the web will stick to the undersurface of the felt by surface tension forces. Commonly, the felt leaves the pickup roll and is conducted in a free run to the first press nip of the press section with the web clinging to its undersurface. After pressing, the web is transferred into the dryer section, which may be made up of a bank of relatively small diameter heated rolls or may be the well known Yankee dryer cylinder, a large diameter heated cylinder. In some types of Fourdrinier machines employed to manufacture tissue and other light weight paper, there may be no press section, and the web is transferred directly to the dryer section. Moreover, most machines employed for tissue and other light grades of paper use a Yankee dryer rather than a series of small dryer rolls.

Particular problems arise in the production of light, thin paper webs of low porosity. The manufacture of such papers on Fourdrinier machines employing a suction couch involves a tendency for the fibers to be sucked hard against the Fourdrinier wire to such an extent that there is a tendency for the fiber to adhere quite firmly to the Fourdrinier wire. When the web is picked off the wire, fibers tend to hang up and remain on the wire with the result of the formation of so called pin holes that are left when fibers are separated from the web and left clinging to the wire. The pin holes, of course, alter the porosity of the paper, and a desired low porosity may be difficult or impossible to achieve when the pin hole problem is encountered.

Another difiiculty with forming thin paper webs is that it is usually advantageous to operate with a stock of relatively low consistency. Because of the low consistency, there is a correspondingly high de-watering action along the wire, and the high de-watering rate and consequent strong flow of water out of the stock and through the Wire tends to cause segregation of the suspension in that the fines in the stock tend to collect on the wire side of the web. The action of the suction couch roll accentuates the tendency for segregation, and the result is a paper web having the characteristic often refered to as two-sidedness.

SUMMARY OF THE INVENTION There is provided, in accordance with the invention, an improved paper-making machine that is particularly well suited for the manufacture of light weight paper webs of the tissue and mono-glazed types and that is capable of producing a high quality, light weight paper at a relatively high running speed. In general, the machine offers particular advantages in manufacturing paper at basis weights of up to about 17 grams per square meter.

A paper-making machine, according to the invention, comprises a forming section having a moving foraminous member adapted to receive and carry a suspension of paper-making fibers in a liquid and to drain liquid from the suspension to form a fibrous web. A rotating, heated Yankee dryer cylinder is mounted in a position such that its surface is in proximate, spaced relation to a point along the path of movement of the foraminous member where the web is to be taken off. A combination rotating suction pick-up, transfer, couch and press roll is positioned in light engagement with the web to engage it against the wire at the pick-up location and is also engaged under dewatering pressure against the web at a nip with the Yankee dryer cylinder. The pick-up roll runs within a felt and preferably has a suction zone that extends substantially continuously from the pickup point on the foraminous member to the press nip with the Yankee dryer cylinder. The machine may include one or more additional press nips formed by felted press rolls that are engaged against the Yankee dryer cylinder at points near and downstream from the combination roll.

The provision, in accordance with the invention, of a felted combination pick-up transfer couch and press roll provides a number of advantages, such as the following:

(1) The web is further de-watered prior to drying on the Yankee dryer cylinder by virtue of the suction from the pick-up point to the press point and by reason of mechanical expression of water at the press nip between the combination roll and the Yankee dryer cylinder. Consequently the web reaches the dryer cylinder at a relatively high dryness, thus reducing the amount of 111018- ture to be removed from the web on the dryer and enabling the machine to be operated at a higher speed (assuming that the dryer is the limiting factor on speed, as it usually is).

(2) The web is maintained under control throughout the transfer from the foraminous member to the dryer, inasmuch as it is held on the transfer felt associated with the combination roll along its entire path of movement during transfer. Accordingly, shut down time resulting from web breaks, a frequent problem in conventional transfer systems in which the web can drop off the underside of a pick-up felt, is substantially eliminated. Moreover, the possibility of disruption in the fiber structure due to distension and flexure that can occur along a free run of a transfer felt is eliminated.

(3) The suction action of the combination roll is applied in a direction that is the reverse of that which normally occurs on a conventional suction couch roll; i.e., the pressure differential established across the web at the combination roll is between a higher pressure on the under side and a lower pressure on the top side of the web. Such reverse suction action reduces the tendency for segregation of the fines of the stock on the underside of the web. Therefore, the machine produces a paper of better quality and more uniform porosity across its thickness than similar paper made on a machine using a suction couch.

(4) The reverse pressure, namely higher pressure below and lower pressure above, generated by the combination roll counteracts the tendency for the web to stick to the wire. As the stock is dewatered along the run of the Fourdrinier wire or other foraminous element, the same tendency for fibers to adhere to the wire is present as is always encountered with a paper former. However, the combination roll, by reason of the reverse suction, tends to pull the web free of the wire and does not accentuate the sticking of the web to the wire, as a conventional suction couch does. As a result, the tendency for pin holes to be formed is materially reduced, to the enhancement of paper quality.

(5) A machine, according to the invention, does not have a separate press section, the web being brought to the dryer on a single transfer felt and pressed onto the smooth surface of the dryer surface. Accordingly, the wire side of the paper, which is the side that is pressed against the surface of the Yankee dryer cylinder, is free of markings from a felt or from markings of knots which may be present in press felts. The freedom of the web from press felt markings on one side contributes to a high quality paper finish and to uniformity of porosity.

(6) The control of the web throughout the transfer from the wire to the dryer cylinder eliminates the problems encountered with transfer systems in which the web is carried on a free run of felt. In such transfer systems, there is a tendency for the web to be stretched during the transfer, thereby altering the fiber structure and consequently the strength and elongation properties of the paper. The suction of the combination roll holds the web and felt securely onto the surface of the roll and substantially eliminates any deformation that could change the fiber structure. Thus, the web is pressed onto the Yankee dryer cylinder with the fiber structure in substantially the same condition as it was at the point that it was picked off the wire, and the machine produces paper having unusually 4 good elongation properties, particularly in the machine direction.

(7) A machine, according to the invention, can be very compact and thus offers a substantial space saving and a consequent cost reduction. Moreover, the cost of manufacturing a single combined pick-up, transfer couch and press roll is substantially less than the cost would be for manufacturing separate, equivalent components separately. Similar savings in maintenance and repairs are afforded, and in general the cost of manufacturing, installing and operating the machine is significantly less than the conventional machines, particularly when spread over the machine output and paid for by the returns from premium quality paper.

DESCRIPTION OF THE DRAWING For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the figures of the accompanying drawings, in which:

FIG. 1 is a schematic side view of one embodiment, components that are in front of the near side frame being illustrated by phantom lines, and the frame and other details not being shown;

FIG. 2 is a schematic side view of another embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Both of the embodiments of the invention illustrated in the two figures of the drawing include a forming section of the Fourdrinier type, and both forming sections, which are designated generally by the reference number 10, are substantially identical to each other. Therefore, the following description of the forming section applies to both embodiments, and the same reference numerals are employed to designate the components of the forming sections 10 of both.

The web forming section 10 includes a headbox 12 that is supplied With a suspension in a liquid of paper-making fibers, usually referred to as the stock, and deposits a layer of stock on an upper, straight, substantially horizontal run of an endless foraminous belt 14. The belt is trained around a breast roll 16 located generally below the headbox, passes over a forming board 18, a pair of table rolls 19, a deflector 20 positioned between the table rolls, and a series of suction boxes 22, all of the last mentioned elements being positioned below the horizontal run and being associated with the formation of a Web on the foraminous belt 14 as liquid is drained and sucked from the stock in the course of moving on the belt from the breast roll toward a drive roll 24. The foraminous belt 14 then is taken back to the breast roll around a series of turning rolls 25, one of which (not shown in detail) is a tension roll and holds the foraminous belt under proper tension. The various components of the Fourdrinier-type forming section 10 described above and illustrated in the drawings, and the functions that they perform, are well known to those skilled in the art, and the details need not be described here. It should be mentioned, however, that it is appropriate to provide a simple, plain roll for the drive roll 24, inasmuch as the roll 24 is not the usual couch or suction couch roll usually found in Fourdrinier type web-forming machines. It will also be readily understood by those skilled in the art that various modifications can be made in the details of the forming section 10, particularly with regard to the arrangement of table rolls, deflectors, suction boxes and the possibility of providing different types of de-watering components in association with the foraminous belt 14.

Both exemplary embodiments of the invention, as illustrated in FIGS. 1 and 2 of the drawings, include a combination suction pickup, transfer, couch and press roll 26, but inasmuch as a modified arrangement of a felt employed with the combination roll is incorporated in the embodiment of FIG. 2, the arrangement of FIG. 2 is described separately hereinafter. In the arrangement of FIG. 1, the combination roll 26 runs within a felt 28 that is, in turn, backed up by a fabric 29, which may be of metallic or synthetic woven material. The felt 28 is lead around a series of appropriately located turning rolls 30 and a tension roll 31 and is led through a felt conditioning device 32 of an appropriate type for cleaning and drying the felt along the run of the felt between the point that it leaves the combination roll 26 and returns to it. The fabric 31 that backs up the felt is turned around a single tension and turning roll 34 and is led through a cleaning and dewatering device, such as a suction box 36.

The combination roll 26 is mounted for rotation on pivoted arms 38 located at the ends of the roll and is positioned in light contact with the web as it is carried on the foraminous member 14 at a pickup point that is designated in FIG. 1 by the reference numeral 40. The pickup point is preferably along an unsupported run of the foraminous belt 14 between the last suction box 22 and the drive roll 24. Furthermore, the combination roll 26 is positioned to form a nip 42 With the surface of a heated Yankee dryer cylinder 44, the Yankee dryer cylinder being located in proximate, spaced relation to the pick-up point 40. A fluid motor 46 or other appropriate device associated with each mounting arm of the combination roll 42 urges the combination roll into de-watering pressure engagement with the Yankee dryer cylinder 44 to squeeze the web against the dryer and to express liquid from the web.

The combination roll 26 is a suction roll and has a suction box 48 that extends from the pick-up point to the press-nip 42.

A second press nip 50 is formed between the Yankee dryer cylinder 44 and a press roll 52 positioned above, downstream of and in proximate relation to the first press nip 42. The press roll 52 runs within an endless press felt 54 that is lead around a series of turning rolls 56 and a tension roll 57 and through a felt conditioning device 58. The felt 54 is backed up by a fabric 60 that runs within it, turns around a turning and tension roll 62 and is led past a conditioning device 64. The press roll 52 is mounted on pivot arms 66 located at its opposite ends and is urged toward the Yankee dryer cylinder 44 by fluid motors 68 or any other suitable operating devices.

The upper part of the Yankee dryer cylinder is enclosed within a hood 70. Guide rolls 72 and 74 are provided adjacent to the output side of the dryer cylinder for guiding the web away from the dryer cylinder and conducting it to winding equipment, another dryer or other apparatus (not shown).

The embodiment of FIG. 2, is for the most part, the same as the embodiment of FIG. 1, the only important difference being the substitution of a single felt 76 that serves both a combination roll 26a and a press roll 52a. Since only a single felt 76 is employed, a number of turning rolls are eliminated, and only one felt conditioner and dryer 78 is employed. Each of the rolls 26a and 52a, however, has an endless back up fabric 80 and 82, respectively, wrapped part way around it within the felt 76. The other components depicted in FIG. 2 are readily identifiable with reference to FIG. 1 and the foregoing description, and the combination roll is also of the same construction as that of FIG. 1.

In the operation of both embodiments, a suspension of paper-making fibers in a liquid, i.e., stock, is deposited on the foraminous belt 14 at the upstream end where the belt passes over the forming board 13. The stock progressively drains as it moves along on the belt and a web is formed. At the pickup point 40, the web is transferred from the foraminous belt 14 onto the felt 28 associated with the combination roll 26 (or 26a) as a result of the differential pressure across the web established by the suction box 48 of the combination roll. The suction in the suction box assists in de-watering the web and also holds the web firmly on the felt 28 (or 78) as the web is transferred from the foraminous belt 14 to the dryer cylinder 44. Consequently, the felt may be run relatively dry so that its ability to take on liquid from the web enhances the dewatering of the web. Moreover, the pressure at the nip 42 between the combination roll 26 and the dryer cylinder 44 may be relatively greater than in the usual first press of a paper-making machine, without a danger of crushing of the web, inasmuch as the moisture content of the web is somewhat reduced by the time the web reaches the press nip 42.

Inasmuch as the surface of the dryer cylinder is smooth, usually a mirror finish, the web will stick to the dryer cylinder when it is pressed against it, and consequently the web is transferred from the belt 28 (or 78) onto the dryer cylinder. An additional pressing operation occurs at the nip 50 between the press roll 52 (or 52a) and the cylinder 44, and following the second pressing, the web continues along on the dryer cylinder 44 and is dried to an extent suflicient that it may be removed in open draw and taken around the guide rolls 72 and 74 for winding, further drying or other operations.

Thus, there is provided, in accordance with the invention, a novel and improved paper-making machine oflfering distinct advantages over machines known heretofore. The machine is capable of producing high quality, lightweight paper at high operating speeds, the paper quality having particularly good characteristics insofar as uniformity of porosity, machine direction strength and elongation properties, and a minimum of the so-called two-sidedness characteristic.

The embodiments of the invention described above are intended to be merely exemplary, and those skilled in the art will be able to make numerous variations and modifications of them without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention, as defined in the appended claims.

I claim:

1. A paper-making machine comprising a forming section having a moving foraminous member adapted to receive and carry a suspension in a liquid of paper-making fibers and to drain liquid from the suspension to form a fibrous web as the suspension progressively moves with the member to a pick-up location along the path of movement of the member, a rotating heated Yankee dryer cylinder positioned with its surface in proximate relation to the said pick-up location along the path of movement of the foraminous member, a combination rotating suction pickmp, transfer, couch and press roll positioned (a) for light engagement at the pick-up location with the web as it is carried on the foraminous member and (b) for engagement under de-watering pressure against the surface of the Yankee dryer cylinder at a press nip with the Yankee dryer cylinder, an endless felt wrapped around a portion of the combination roll, such portion extending at least from the pick-up location to the press nip, and means for urging the combination roll against the dryer cylinder with a pressure suificient to express liquid from the web at the press nip.

2. A paper-making machine according to claim 1 wherein the combination roll is a suction roll having a suction zone that extends substantially continuously from the pick-up location to the press nip.

3. A paper-making machine according to claim 1 and further comprising a press roll positioned to form a second press nip with the Yankee dryer cylinder at a location proximate to and downstream, relative to the direction of rotation of the cylinder, from the first press nip, a paper-making felt wrapped around a portion of the press roll that includes the second press nip, and means for urging the press roll against the Yankee dryer 7 cylinder under pressure sulricient to express liquid for the web.

4. A paper-making machine according to claim 3 wherein there is a single paper-making felt wrapped partly around both the combination roll and the press roll.

5. A paper-making machine according to claim 1 wherein the foraminous member is an endless flexible belt having a substantially straight and horizontal run on which the suspension is deposited and the Webformed.

6. A paper-making machine according to claim 5 wherein the pick-up location is along a free and unsupported section of the belt.

7. A paper-making machine according to claim 6 wherein the pick-up location is along the straight and horizontal run of the belt.

References Cited UNITED STATES PATENTS 2,732,772 1/1956 Hornbostel 162-359 X 1,347,723 7/1920 Wagner 162290 HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 

